Generally speaking, the converters may be divided into two types depending on their modulation methods. One is a pulse width modulation (PWM) converter, and the other is a pulse frequency modulation (PFM) converter. The two different types of converters have their respective advantage and disadvantage. The PWM converter, such as a phase shift full bridge (PSFB) converter, may output a voltage in a wide range. However, the PWM converter can't realize soft switching conditions for all devices, which makes it impossible to obtain high frequency and results in a relatively large size. The PFM converter, such as a series resonant (LLC) converter, may realize soft switching conditions for all devices, that making it possible to obtain high efficiency and high frequency and to minimize the size of the converter. However, the PFM converter could only output a voltage in a narrow range. This is because other characteristics, such as high efficiency, of the PFM converter would be lost if the PFM converter outputs a voltage in wide range.
In an application of an electric vehicle charging station, a charging device is required to be an isolated converter. The isolated converter generally demands an output voltage in a wide range of 200-1000 V, and a power in a range of 50-300 kW. It has become a major challenge to increase the efficiency and minimize the size of the charging device.
An object of the present disclosure is to provide a novel combining and controlling method of converters for achieving high efficiency and optimized size while outputting a voltage in a super wide range.